Category Archives: green

GOLDSTEIN: John is not rich and he is not getting solar panels to save the world.

Does the environmental part of it – is that meaningful to you? Does that matter?

O’HAGAN: Not really. (Laughter).

GOLDSTEIN: If you were an environmentalist or if you just like solar power, John O’Hagan is your dream come true. John O’Hagan is the revolution you’ve been waiting for. He’s – he is not getting solar power for a moral or philosophical reason. He’s not doing it ’cause he’s worried about climate change. John O’Hagan is getting solar power because it’s cheap.

So for the most recent bill it was 5.1 therms/day and 19F avg
Last bill: 4.0 therms/day and 29F avg.

Does it make sense? Yes! If we make the assumptions that:

1) 99% of our gas use is for heating and not
– hot water heater
– stove and oven
– clothes dryer (gas)

2) An average inside temp over the course of day and night is roughly 65F

Then
DeltaT= 65F-19F=46F with 5.1 therms per day
DeltaT= 65F-29F=36F with 4.0 therms per day

46/36 = 1.28
5.1/4.0 = 1.28

Or another way:

46/5.1 == 36/4.0 => 9.0 dT for each 1 therm

The ratios are the same! This is a little too good to be true. Probably some luck in my assumptions and guess of 65F. But in any case, that’s roughly what you would expect.

So IOW, if you want to keep your gas bill constant when it gets much colder outside, just keep it colder inside by an equal amount (to keep your deltaT constant) and you should do ok!

The only problem with this (besides not being able to wear more sweaters and hats at some point) is that you should be careful (if your house is like mine and colder in some spots) that you don’t cause some pipes to freeze in that already cold bathroom. Unlikely for most houses, but possible.

To truly tell which winters have been the worst, I propose a variation on the HDD (heating degree days… along with cooling degree days, great tools for comparing climates) calculation of “snow depth days” that also includes a multiplier of air temp (or maybe even adjusted for wind chill). http://www.wermenh.com/sdd/ne-1415.html

Or maybe the temperature should be an inverse of some sort, so good winters would be lots of snow, but also somehow mild temps.

1.9 stars. Typical 1-star review excerpt: “I’d like to discuss this matter with the numb-skull who though that it would be more friendly to the polar bears to pour gas all over oneself rather than venting the can as it has been done for years…through a vent hole.” LINK

So stick with the vent hole method if possible! 1 spill is worth 1000 ventings. Go with the ventings.

“66. I’m going back to post #38 about minisplit capacity and dewpoint. The information in that post contradicted what I understood to be correct, so I checked in with my engineering contact at Mitsubishi. Here’s what he wrote:
“The only relevant factor in determining the available heating capacity is the outdoor wet bulb temperature. This graph below represents guaranteed heating capacities at various wet bulb temperatures.”
This graph shows that the Hyperheat models FE09 and FE18 produce 100% of their nominal capacity down to about 3F wet bulb, and the FE12 down to about 12F wet bulb (I’m eyeballing this graph). In the case of the FE18, I take this to be the capacity they publish at 47F dry bulb, 21,600 BTU/hour, which they show as the maximum capacity in their submittal sheet at 5F dry bulb as well. This graph states that it includes the correction for defrost.
He goes on to say:
“Rated capacity is the capacity as the equipment was tested in a lab setting to obtain the published efficiency values, maximum capacity is the actual capacity that the unit is capable of producing as it operates in the field, you should always use maximum capacity when selecting/sizing equipment for an application.”
So I don’t believe people need to be concerned about dewpoint of the outdoor air when sizing the Mitsubishi Hyperheats. Of course, at temperatures approaching 0F, the wet bulb and the dewpoint get closer together than they do at higher temperatures.”

I would also add my 2 cents to the comments at the article about heating a house solely with minisplits:

Point source heating works is fine. You can really compare minisplits to a wood stove, because there is almsot 0 temperature differential, which is frustrating because one can’t cozy up to a minisplit, or dry soaking wet clothes after sledding, or keep one room warmer or cooler than others.

Point source cooling is a bigger problem especially if you are co-sleeping and have 4 people in one room because that’s a lot of body heat and if you don’t have a minisplit right in the room it’s less than ideal in the summer even with the door open. 1 or 2 people was fine, even better if one switched the HRV direction I bet! Good idea.

… I like the idea of doing exhaust for ERV/HRV from bedrooms. That would probably be a good idea. Luckily it’s also easy to reroute the supply/exhaust ducts so an easy retro-project.

Even R-5 windows are cool in the winter if you have a small room and you a sitting or sleeping right next to one.

we never had problems with 0F heating even though our minisplits were only rated for 5F.

On the topic of back-up heat, I would probably go for a wood stove and off-grid/hybrid/grid tie solar PVs if I were still in the house. An all-electric house is kinda frustrating when the power goes out and it’s bright and sunny after the storm and your grid-tie PVs can’t do anything. 🙂 Those little honda generators seem nice but I hate changing oil/maintaining stuff. But honestly, a $50 inverter attached to a car battery ran the fridge just enough to keep things over a 4 day outage. So how much money does one really want to throw at a minimal problem? A cooler in the car would have worked fine too since it was winter, and it’s not bear country.

Parts can take a little while with a minisplit (control boards), but luckily things rarely happen. Our residential mitsu model was difficult to debug I guess (commercial models might have better troubleshooting tools?) so it was one easier to just replace a whole compressor unit.

Was minorly annoyed I couldn’t set back our mitu system below 59F I think it was for when we were occasionally away. Not that lower would have added up to much in $.

OK, other than that… minisplits in a superinsulated house were fine. Silent (as I sit here and listen to my current noisy forced-hot air system). Comfortable. Cheap/almost non-existent bills.

OK that’s it. Just wanted to chime in a little with little pros and cons.